Hospitalization rates of infants due to whooping cough were generally significantly lower after recommendations were expanded to advise all adolescents to receive the Tdap vaccine.
Increased vaccine coverage against whooping cough among adolescents has helped reduce the number of infants hospitalized with the disease, a new study suggests.

In 2006, the recommendation for the tetanus-diphtheria-acellular pertussis (Tdap) vaccine was expanded to include all adolescents, who often spread pertussis to infants. As a result, more teens were vaccinated, and by 2011, 78% of Americans aged 13 to 17 had received the Tdap vaccine. The study, published online on October 21, 2013, in Pediatrics, evaluated the effect of this increase in vaccination coverage by analyzing hospitalization rates for infants with whooping cough before and after the recommendation change.

Infants aged younger than 1 year who were diagnosed with pertussis from 2000 to 2010 were identified in the Nationwide Inpatient Sample and included in the analysis. Hospitalization rates from 2000 to 2005, before the recommendation change was implemented, were used to estimate what the hospitalization rates from 2008 to 2011 would have been if the recommendations had not been expanded. These results were then compared with the actual observed rates of infant hospitalization due to pertussis from 2008 to 2011. Results were adjusted using data from the US Census Bureau to represent annual national population hospitalization rates. Data from 2006 and 2007 were not included in the analysis, allowing time for the expanded vaccination recommendation to take effect.

During the period before the universal adolescent Tdap recommendation, the rate of infant hospitalization due to pertussis increased by an average of 0.64 discharges per 10,000 infants each year. The results indicate that after the vaccine was recommended for all adolescents, observed hospitalization rates were significantly lower than expected in 2008, 2009, and 2011. In 2011, approximately 3.27 infants per 10,000 were hospitalized with pertussis, compared with the estimated 12 hospitalizations per 10,000 infants that would have occurred if the vaccination recommendation had not been expanded. In 2010, however, the observed number of hospitalizations was not significantly different from the expected rate.

The researchers also studied the characteristics of the infants hospitalized and the cost of their care. They found no significant difference between the average age of infants or the portion of infants with life-threatening cases of whooping cough before and after the adolescent Tdap recommendation went into effect. Length of stay did decrease slightly after the recommendation, which is consistent with trends for other respiratory illnesses in infants. The results also indicated that the average hospitalization cost for these infants increased significantly from 2000 to 2011, even after accounting for inflation.

The findings suggest that increased adolescent Tdap vaccination may have contributed to decreases in somewhat severe pertussis cases among infants. However, the effects of the vaccine were not strong enough to reduce the rate of hospitalization during the 2010 outbreak. Given the risks and the increasing cost of treating whooping cough in infants, the authors suggest that increased vaccination is needed to further reduce the burden of the disease.

“Further Tdap vaccination efforts among adolescents, and likely adults as well, are needed to prevent infant hospitalization on a more consistent basis,” they write.